1. Field of the Invention
The present invention relates to a gas storage container. In particular, the present invention relates to a gas storage container, which accommodates a gas absorbing/adsorbing material therein.
2. Description of the Related Art
As is well known, a fuel cell generates electric power by supplying a fuel gas such as hydrogen to an anode, while supplying an oxygen-containing gas such as oxygen to a cathode. Therefore, for example, a fuel cell vehicle that accommodates the fuel cell carries a gas storage container thereon, which is filled with hydrogen. The fuel cell vehicle runs by using reaction gases made up of atmospheric air, which serves as the oxygen-containing gas, and hydrogen supplied from the gas storage container.
As clearly appreciated from this fact, the larger the hydrogen-accommodating amount of the gas storage container is, the longer the distance that the fuel cell vehicle can successfully run over is. However, if an excessively large gas storage container is carried by the vehicle, the weight of the fuel cell vehicle increases. Consequently, an inconvenience arises in that the load on the fuel cell also is increased. From this viewpoint, various trials have been made in order to improve the hydrogen-accommodating amount, while maintaining a small volume for the gas storage container. As one technique therefor, for example, it has been pointed out that a substance (hereinafter referred to as a “gas absorbing/adsorbing material”), which occludes or adsorbs the gas and which is represented by a hydrogen absorbing alloy, may be accommodated within a container, as described in Japanese Laid-Open Patent Publication No. 2004-108570.
In the case of the gas storage container described in Japanese Laid-Open Patent Publication No. 2004-108570, a powdery hydrogen absorbing alloy is accommodated, as is, inside the container. In general, a reaction whereby the gas absorbing/adsorbing material occludes or adsorbs the gas is an exothermic reaction. Further, when the container is filled with the gas, it is accompanied by adiabatic compression. Therefore, when the gas storage container is filled with hydrogen gas, if the temperature inside the container increases excessively, the occlusion or adsorption of gas by the gas absorbing/adsorbing material is inhibited. Of course, when such a situation arises, the gas accommodating amount also decreases.
In view of the above, it has also been suggested in Japanese Laid-Open Patent Publication No. 2004-108570 that a heat exchanger may be arranged in a substantially central portion of a container, in order to suppress a temperature rise within the container.
On the other hand, it has been suggested in Japanese Laid-Open Patent Publication No. 2001-145832 that a phase changing substance, which induces absorption and release of latent heat depending on a change in temperature, may be enclosed within microcapsules, thereby providing a heat storage material. The heat storage material is accommodated within the container after being mixed with the gas adsorbing material. In this case, it has been affirmed that heat, which is generated when the container is filled with gas, can be absorbed by the heat storage material.
Even if a heat absorbing material or substance is arranged inside the container, as described in Japanese Laid-Open Patent Publication Nos. 2004-108570 and 2001-145832, when gas is introduced into the container, which is filled with a powdery gas absorbing/adsorbing material, from a charging port provided at an upper portion of the container, the gas absorbing/adsorbing material, which is disposed at an upper position, begins to occlude or adsorb the gas. That is, it is impossible to avoid the occurrence of portions therein, which exhibit high temperatures locally within the container. When such a situation arises, portions, which exhibit differing amounts of thermal expansion, arise in the container in some cases. In this case, depending on the situation, there is a concern that an outer shell and a liner, which make up parts of the container, may become exfoliated from each other.
When a heat exchanger is provided, it is inevitable that the heat exchanger must be large in size, in order to avoid the occurrence of such high temperature portions. Due to this fact, the volume and weight of the container must be increased as well.
On the other hand, when a heat storage material is accommodated therein, there is a concern that heat absorption thereby may still be insufficient, due to the high temperature produced locally inside the container. Therefore, in order to reliably absorb heat, a large amount of the heat storage material must be used. However, the heat storage material does not contribute to occlusion and/or adsorption of the gas at all. Therefore, in order to increase the gas-accommodating amount, while utilizing a large amount of the heat storage material, it also is necessary to increase the overall volume and weight of the container.
As described above, an inconvenience arises in that the volume and weight of the container are inevitably increased, in order to avoid high temperatures from occurring during filling of the container with gas.